The present invention is directed to a vibration meter having a pressure sleeve.
German Patent No 44 03 660 discusses a vibration meter having a pressure sleeve which is used as a knock sensor for monitoring the function of an internal combustion engine in a motor vehicle, This pressure sleeve is fixedly mounted via a bearing surface on the component causing the vibrations, in this case to the engine block of the internal combustion engine.
With this arrangement, the vibrations to be detected are knocking sounds of the internal combustion engine during operation. The sounds are transmitted via the pressure sleeve to a piezoceramic disk as the actual sensor element, which has interposed contact disks and insulating disks allowing the signal pick-up, and in this manner an analyzable output signal is generated.
The manner of mounting or clamping of this sensor arrangement on the pressure sleeve and the mounting of the vibration meter on the vibrating component may have a considerable influence in this case not only on the method of manufacture but also on potential faulty measurements and interferences in operation. In the case of this known vibration meter, the clamping of the sensor element having a plurality of component parts, such as a spring and a seismic mass, is accomplished with a ring nut, for instance, which is capable of being screwed onto a corresponding threat on the pressure sleeve.
When mounting this vibration meter with the aid of an axially acting screw on the component causing the vibrations, the base surface of the pressure sleeve, which is concave from the outside toward the center bore, is pressed onto the surface of the component lying across from it. As a result of this pressure, the bearing surface of the pressure sleeve lying opposite inside, which supports the sensor element, also assumes the same angle at which the bottom surface runs concavely. Thus, a cavity may form between the bearing surface and the sensor arrangement, and here, in particular, the ceramic disk with the insulation and contact disks, in the region lying radially on the inside.
Since compensation for this cavity by elastic deformation of the relatively rigid sensor components is generally minimal, an optimal introduction of the vibrations to the actual sensor arrangement via the pressure sleeve is made more difficult.
The vibration meter having a pressure sleeve in which the pressure sleeve is mountable under pressure on a component causing vibrations using an initially concave bottom surface is refined according to an exemplary embodiment of the present invention in that the bearing surface for a sensor arrangement, which may be supported on a bearing surface of the pressure sleeve situated inside of and opposite to the bottom surface, prior to mounting, may have a contour, which may run radially inward in a convex manner. The contour of the bearing surface may be dimensioned such that the sensor arrangement lies essentially flat on the bearing surface after mounting.
The bottom surface, which may have the concave contour prior to mounting, may be changed by the pressure of the mounting, usually via a screw guided through the center bore. In an exemplary embodiment, the angles at which the bottom surfaces are concave and the bearing surface is convex, may be approximately identical prior to mounting, in the range of 10xc2x0 to 20xc2x0, for instance, so that they always run in a parallel manner.
In this way, a flat resting surface for the sensor arrangement may also be produced in a particularly advantageous manner after the vibration meter is mounted, due to the described treatment of the bearing surface and the bottom surface. In this case, the essential components of the sensor arrangement for a knock sensor to be used as a vibration meter may be a piezoceramic for generating an electrical signal and a superposed seismic mass, whose surfaces thus may always lie on top of one another in a plan-parallel manner.